This invention relates to apparatus for measuring the gage of any given track, and more particularly, to apparatus which can be affixed to revenue producing trains which pass over the tracks in question and provide electrical signals representative of the gage of the track while the train travels at high speeds.
The gage of a pair of rails is defined as the distance between the rails measured at a point five-eighths of an inch below the top surface of the rail heads. Standard gage is specified as 561/2 inches. While there are some exceptions to this the great majority of rail systems use standard gage. Regardless of what gage system is in use, a major cause for concern is when the gage due to wear, faulty construction or any other reason becomes enlarged. With standard gage, no track should be permitted a gage enlarged more than one inch and a quarter.
With the advent of high speed commuter traffic between the various communities some means must be provided to measure the gage of the rails forming the track on a regular basis. Such information would enable the appropriate parties to schedule maintenance of the rails because the gage is an important factor relating to condition of the rails. Apparatus which would permit this to be accomplished rapidly and on a continuous basis would avoid tragic derailments and other accidents associated with deteriorating foundations supporting the tracks in question.
Prior art devices for measuring the gage of railroad track from fast moving railroad trucks have comprised primarily a pair of proximity sensors spaced a fixed distance apart and each observing one of the rails. Such devices have suffered from a number of disadvantages including requirements for moving parts, inadequate response times, complicated alignment procedures, etc.
Specific types of proximity sensors that have been developed for this purpose include capacitive, magnetic and electro-optical sensors. The capacitive or magnetic sensors suffer from poor sensitivity at large air gaps and measurement distortions caused by rail components such as rail webs and rail bases that are extraneous to gage. Although this problem can be overcome by servo-driven gage sensors that maintain a small air gap regardless of gage variations, the resultant moving parts present longevity problems in the rugged rail environment.
Many of the above problems are obviated by an electro-optic sensor disclosed in U.S. Pat. No. 3,864,039. The system disclosed in that patent floods the inside base of the rail with light and detects the position of the shadow boundary between the rail head and the illuminated base, via an electro-optical detector mounted on the truck above the rail head. The position of the shadow boundary represents the innermost location of the rail head which represents gage in an absolute sense, i.e., the minimum distance between the rails. It does not, however, represent effective gage as defined by the track standards established by the Department of Transportation/Federal Railroad Administration. It also senses joint bars on jointed rail which protrude into the profile being measured. As noted above, those track standards define gage as the distance between the rails measured in a plane that is five-eights of an inch below the top of the rail heads. This is a more practical definition than minimum distance which can be affected by thin overhanging lips that develop on the inside profile of rail heads. Such a condition often occurs on the low rail of curved track and the resultant lip is ineffective to support the wheel of a railroad truck. Thus, a gage measurement influenced by such a lip provides a false sense of security in terms of safety. Similarly, a rail badly worn along its upper surface but of normal width at the base of the rail head establishes a minimum distance between rails that would indicate safer track than is actually the case.
The object of this invention, therefore, is to provide an improved, relatively simple device that accurately measures rail gage in a plane that is five-eighths of an inch below the top of the rail heads, is easy to align and requires no moving parts.